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Viruses
There are over 400 viruses known to attack humans, virus are basically "protein packages" (Graham 2009) that contain either RNA or DNA nucleic acid and the viral enzymes necessary to transcribe and replicate the viral genome. Viruses are believed to cause the majority of acute respiratory infections in both adults and children. (Shigeta 1998) Every living thing on the planet has a virus that infects it, as diverse in themselves as the hosts they invade. (Jones 2004) http://en.wikipedia.org/wiki/Virus_classification#Baltimore_classification There are 7 "types" defained by the Baltimore classification (first defined in 1971) is a classification system that places viruses into one of seven groups depending on a combination of their nucleic acid (DNA or RNA), I: dsDNA viruses II: ssDNA viruses III: dsRNA viruses IV: (+)ssRNA viruses V: (−)ssRNA viruses VI: ssRNA-RT viruses VII: dsDNA-RT viruses as few as N genes, smallpox 300 gene, minivirus 900? 3-4 proteins, largest 100 proteins. The complete strucutre of the virus including the capsid and the coat, and any viral proteins is called a virion. In 1967 the US surgeon general announced that infectious diseases were no longer a problem @todo 1967 (patrick 2009) in the early 1980s in the UK, there was serious consideration given to closing university virology departments (patrick 2009) The WHO estimates 1.8 million AIDs deaths in 2010, and influenza and SARS ;http://www.who.int/gho/mortality_burden_disease/causes_death_2008/en/index.html @todo size of a virus comparison viruses can infect bacterial cells, and are called macrophages many younger people have little immunity to asian flu, hence pandemic might effect younger people. zoonotic infections (from animal to man) cause such concern because if the virus infection does take hold then it does so within a virgin population. No existing immunity to the virus will exist in the new species and virus replication can proceed unchecked with devastating results. It is believed that Spanish flu is an zoonotic infection from poultry or pigs @todo The tobacco mosaic virus was described in the 1930s, which led to ther realization that similar agents could infect animals. Enders, Weller and Robbins identified the Poliovirus (RNA virus), the first human virus to be characterized ;virus shedding: @todo ;antigenic constituents: @todo Transmission viruses can be spread by air through sneezing and coughing, or via a vector such as a tick or parasite. Virus vary in their hardy-ness and some can only survive for a short time away from a host, and some viruses can last for long periods and are transmitted through food or contimated water supplies. West nile fever is believed to be spread by mosquito bites. Structure capsid self-assembly nucleo-capsid protomers viral nucleic acid the virus particles contain the viral genome, along with functional proteins, and a protective coat. the coat is comprised of protein, or a phospholipid envelope with embedded proteins the surface components of the virus interact with the target host cell, resulting in attachment of the particle to the host target cell surface. Viral Enzymes Viral polymerases are used to transcribe the viral nucleic acid into a form that takes advantage of the host cell ribosomal infrastructure. Some viruses possess reverse transcriptase, which is an enzyme which converts RNA to DNA Some virus encode their proteins into a single polypeptide, which is then cleaved by a protease into functional components. This process offers a drug target for inhibitory effects. lifecycle There are 5 basic steps in the virus life cycle # adsorption: the virus binds to the surface of the host cell, by targeting some surface protein # penetraion and uncoating: the virus crosses the cell bi;ipid layer and delivers the viral nucleic acid into the cytoplasm # replication and transcription # synthesis and assemby # maturation and virion release Challand; # attachment # followed by fusion with (or penetration of) the cell membrane # thereby liberating the core components of the virus into the cell interior # viral enzume control synthesis of new virus nucleic acid # reassembly takes place # budding releases virus # non-enveloped viruses remain in the cell until the latter is exhausted # cell death causes the cell to break open and release virus progeny into extracellular environment Cytotoxicity eventually the virus kills the host cell via depletion of materials and energy? The immune system response to the foreign material of the virus project many of the symptoms of infection immunoresponse all virus have surface proteins that can be recognised the host can produce antibodies to the virus particles the body "remembers" the viral antigen and has circulating antibodies prepared. immunity remains unless the virus undergoes sufficient antegenic drift, or more significantly antigenic shift Vacination the body is intriduced to the virus by some inactivated form in order to generate entigen Treatment See main article Antiviral_agents most antiviral agents targetting DNA viruses are inhibitors of DNA polymerase HIV has spurred the development of a variety of treatements targetting various stages of the virus life cycle. resistance is a problem with most antiviral drugs due to the mutability of the virus genome Broad spectrum antivirals A class of drugs working on common viral traits, like mutability, could offer a general treatment for viruses much like antibiotics offer for bacterial infection (Jones 2004) viruses @todo families of viruses, genus of virus, species type example. Acute respiratory infections Viruses are believed to cause the majority of acute respiratory infections (ARI) in children. (Shigeta 1998) these include Influenza A, B, C syncytial virus (RSV) ortho-myxoviruses para-myxoviruses list ;Tobacco mosaic virus: was described in 1930s ;Poliovirus: first human virus to be characterized (and RNA nucleic acid) ;HIV: Human immunodeficiency virus ; ebola (haemeregic fever): ; smallpox: eradicated by vaccinations, paramyxovirus equine morbillivirus Mumps measles small pox cow pox influenza Cox-sackievirus Category:Infectious Disease Category:Viruses